Hydrogel particles with tunable optical properties

ABSTRACT

The present disclosure relates to compositions comprising a hydrogel particle with optical properties substantially similar to the optical properties of a target cell, and methods for their use.

1. CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of provisional application No. 61/621,376, filed Apr. 6, 2012 and of provisional application No. 61/668,538, filed Jul. 6, 2012, the contents of each of which are incorporated herein in their entireties by reference thereto.

2. BACKGROUND

Flow cytometry is a technique that allows for the rapid separation, counting, and characterization of individual cells and is routinely used in clinical and laboratory settings for a variety of applications. The technology relies on directing a beam of light onto a hydrodynamically-focused stream of liquid. A number of detectors are then aimed at the point where the stream passes through the light beam: one in line with the light beam (Forward Scatter or FSC) and several perpendicular to it (Side Scatter or SSC). FSC correlates with the cell volume and SSC depends on the inner complexity of the particle (i.e., shape of the nucleus, the amount and type of cytoplasmic granules or the membrane roughness). As a result of these correlations, different specific cell types exhibit different FSC and SSC, allowing cell types to be distinguished in flow cytometry.

The ability to identify specific cell types, however, relies on proper calibration of the instrument, a process that has relied on the use of purified cells of the cell type of interest. Obtaining these purified cells can require costly, laborious procedures that are prone to batch-to-batch variation. Therefore, there is a need in the art for synthetic compositions with tunable optical properties that can mimic specific cell types in devices such as flow cytometers.

3. SUMMARY

In one aspect, the present disclosure provides for compositions comprising a hydrogel particle, wherein the hydrogel particle has at least one optical property substantially similar to that of a target cell, wherein the optical property is measured by a cytometric device. In another aspect, the present disclosure provides for methods of producing a hydrogel particle, wherein the hydrogel particle has optical properties substantially similar to the optical properties of a target cell. The present disclosure also provides for methods of producing a hydrogel particle, wherein the hydrogel particle has pre-determined optical properties. Also provided for is a method of calibrating a cytometric device for analysis of a target cell, the method comprising a) inserting into the device a hydrogel particle having optical properties substantially similar to the optical properties of the target cell; b) measuring the optical properties of the hydrogel particle using the cytometric device, thereby calibrating the cytometric device for analysis of the target cell.

4. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the optical properties of disclosed hydrogel particles compared to polystyrene beads;

FIG. 2 depicts the process of producing labeled hydrogel particles of the disclosure;

FIG. 3 provides brightfield and fluorescent images of labeled hydrogel particles of the disclosure; and

FIG. 4 illustrates the use of hydrogel particles of the disclosure as calibrants for cell types displaying a variety of optical scattering properties.

FIG. 5 provides dating showing correlation of inter-drop delay for a flow cytometer with hydrogel particle diameter.

FIG. 6 provides brightfield (6A and 6C) and fluorescent (6B and 6D) images of Chinese Hamster Ovary cells (6A and 6B) and hydrogel particles of the disclosure (6C and 6D).

FIG. 7 provides data showing comparison of human buccal cells to hydrogel particles encapsulating different amounts of DNA, as measured by fluorescence-activated cell sorting (FACS).

FIG. 8 provides data for hydrogel particles encapsulating nanoparticles at different concentrations, demonstrating tuning of side scattering independent of forward scattering.

FIG. 9 provides data for hydrogel particles produced with different percentages of polymer, demonstrating tuning of refractive index measured by forward scattering.

5. DETAILED DESCRIPTION 5.1. Definitions

As used herein throughout the specification and in the appended claims, the following terms and expressions are intended to have the following meanings:

The indefinite articles “a” and “an” and the definite article “the” are intended to include both the singular and the plural, unless the context in which they are used clearly indicates otherwise.

“At least one” and “one or more” are used interchangeably to mean that the article may include one or more than one of the listed elements.

Unless otherwise indicated, it is to be understood that all numbers expressing quantities, ratios, and numerical properties of ingredients, reaction conditions, and so forth, used in the specification and claims are contemplated to be able to be modified in all instances by the term “about”.

5.2. General Overview

Several critical calibration measurements for flow cytometers require precise time resolution, such as setting the offset time between lasers, and calculating the delay time between detection and sorting of an object. Due to the fluidic conditions within the instrument, precise setting of these timing parameters requires the use of calibration particles that are the same size as the cells to be analyzed. Timing calibrations are typically performed using polystyrene beads with variable fluorescent intensities to calibrate the response of an excitation source and to set the inter-laser timing delay and sorting delay. Flow cytometers can also be calibrated using forward and side scatter signals which are general measures of size and granularity or complexity of the target sample. These calibrations are crucial for the accurate performance of the cytometer and for any downstream analysis or sorting of cell populations. The disclosed hydrogel particles exhibit tuned scatter properties and are suitable for use as calibration reagents for a range of mammalian or bacterial cell types. Scattering is a standard metric for distinguishing cell types in heterogenous mixtures for clinical, food safety, and research purposes.

Although polystyrene particles can be used to set inter-laser and sorting delays for some applications, many eukaryotic cell types fall outside of the size range of commercially available polystyrene particles (1-20 μm) making it nearly impossible to accurately calibrate a flow cytometer for these targets. Also, as shown in FIG. 1, polystyrene particles are fundamentally limited in the optical properties that can possess such as side scattering, which is a general measure of cellular complexity. Polystyrene particles are therefore limited in the two most important passive optical measurements used in flow cytometry: FSC (forward scattering), and SSC (side scattering) which measure the size and complexity of the target respectively. Due to these limitations of polystyrene, users must rely on purified cell lines to calibrate fluorescent intensity, inter-laser delay, sort delays, size and cellular complexity for experiments. This is a lengthy and labor-intensive process that increases the cost of flow cytometry validation and research pipelines significantly. More importantly, these calibration cell lines introduce biological variation, causing disparities in the interpretation of data.

Accordingly, the present disclosure provides for compositions comprising a hydrogel particle, wherein the hydrogel particle has optical properties substantially similar to the optical properties of a target cell. The inventors have unexpectedly discovered that optical properties of a hydrogel particle can be independently modulated by altering the composition of the hydrogel particle. For example, side scattering (SSC) can be modulated without substantially affecting forward scattering (FSC), and vice versa. Furthermore, the optical properties (e.g. refractive index) of hydrogel particles can be tuned without having a substantial effect on density of the particle. This is a surprising and useful feature, as hydrogel particles that serve as surrogates for cells in cytometric methods such as flow cytometry or (fluorescence-activated cell sorting) FACS require a minimal density in order to function in those assays.

The present disclosure also provides for methods of producing a hydrogel particle, wherein the hydrogel particle has optical properties substantially similar to the optical properties of a target cell. The present disclosure also provides for methods of producing a hydrogel particle, wherein the hydrogel particle has pre-determined optical properties. Also provided for is a method of calibrating a cytometric device for analysis of a target cell, the method comprising a) inserting into the device a hydrogel particle having optical properties substantially similar to the optical properties of the target cell; b) measuring the optical properties of the hydrogel particle using the cytometric device, thereby calibrating the cytometric device for analysis of the target cell. Cytometric devices are known in the art, and include commercially available devices for performing flow cytometry and FACS.

5.3. Hydrogels

Hydrogel particles of the disclosure comprise a hydrogel. A hydrogel is a material comprising a macromolecular three-dimensional network that allows it to swell when in the presence of water, to shrink in the absence of (or by reduction of the amount of) water but not dissolve in water. The swelling, i.e., the absorption of water, is a consequence of the presence of hydrophilic functional groups attached to or dispersed within the macromolecular network. Crosslinks between adjacent macromolecules result in the aqueous insolubility of these hydrogels. The cross-links may be due to chemical (i.e., covalent) or physical (i.e., Van Der Waal forces, hydrogen-bonding, ionic forces, etc.) bonds. While some in the polymer industry may refer to the macromolecular material useful in this invention as a “xerogel” in the dry state and a “hydrogel” in the hydrated state, for purposes of this patent application the term “hydrogel” will refer to the macromolecular material whether dehydrated or hydrated. A characteristic of a hydrogel that is of particular value is that the material retains the general shape, whether dehydrated or hydrated. Thus, if the hydrogel has an approximately spherical shape in the dehydrated condition, it will be spherical in the hydrated condition.

Disclosed hydrogels can comprise greater than about 30%, greater than about 40%, greater than about 50%, greater than about 55%, greater than about 60%, greater than about 65%, greater than about 70%, greater than about 75%, greater than about 80%, greater than about 85%, greater than about 90%, or greater than about 95% water. Synthetically prepared hydrogels can be prepared by polymerizing a monomeric material to form a backbone and cross-linking the backbone with a crosslinking agent. Common hydrogel monomers include the following: lactic acid, glycolic acid, acrylic acid, 1-hydroxyethyl methacrylate, ethyl methacrylate, propylene glycol methacrylate, acrylamide, N-vinylpyrrolidone, methyl methacrylate, glycidyl methacrylate, glycol methacrylate, ethylene glycol, fumaric acid, and the like. Common cross linking agents include tetraethylene glycol dimethacrylate and N,N′-methylenebisacrylamide. In some embodiments, a hydrogel particle of the disclosure is produced by the polymerization of acrylamide.

In some embodiments, a hydrogel comprises a mixture of at least one monofunctional monomer and at least one bifunctional monomer.

A mono functional monomer can be a mono functional acrylic monomer. Non-limiting examples of mono functional acrylic monomers are acrylamide; methacrylamide; N-alkylacrylamides such as N-ethylacrylamide, N-isopropylacrylamide or N-tert-butylacrylamide; N-alkylmethacrylamides such as N-ethylmethacrylamide or N-isopropylmethacrylamide; N,N-dialkylacrylamides such as N,N-dimethylacrylamide and N,N-diethyl-acrylamide; N-[(dialkylamino)alkyl]acrylamides such as N-[3dimethylamino)propyl]acrylamide or N-[3-(diethylamino)propyl]acrylamide; N-[(dialkylamino)alkyl]methacrylamides such as N-[3-dimethylamino)propyl]methacrylamide or N-[3-(diethylamino)propyl]methacrylamide; (dialkylamino)alkyl acrylates such as 2-(dimethylamino)ethyl acrylate, 2-(dimethylamino)propyl acrylate, or 2-(diethylamino)ethyl acrylates; and (dialkylamino)alkyl methacrylates such as 2-(dimethylamino)ethyl methacrylate.

A bifunctional monomer is any monomer that can polymerize with a monofunctional monomer of the disclosure to form a hydrogel as described herein that further contains a second functional group that can participate in a second reaction, e.g., conjugation of a fluorophore.

In some embodiments, a bifunctional monomer is selected from the group consisting of: allyl amine, allyl alcohol, allyl isothiocyanate, allyl chloride, and allyl maleimide.

A bifunctional monomer can be a bifunctional acrylic monomer. Non-limiting examples of bifunctional acrylic monomers are N,N′-methylenebisacrylamide, N,N′-methylenebismethacrylamide, N,N′-ethylenebisacrylamide, N,N′-ethylenebis-methacrylamide, N,N′propylenebisacrylamide and N,N′-(1,2-dihydroxyethylene)bisacrylamide.

Higher-order branched chain and linear co-monomers can be substituted in the polymer mix to adjust the refractive index while maintaining polymer density, as described in U.S. Pat. No. 6,657,030, incorporated herein by reference in its entirety.

In some embodiments, a hydrogel comprises a molecule that modulates the optical properties of the hydrogel. Molecules capable of altering optical properties of a hydrogel are discussed further below.

Naturally occurring hydrogels useful in this invention include various polysaccharides available from natural sources such as plants, algae, fungi, yeasts, marine invertebrates and arthropods. Non-limiting examples include agarose, dextrans, chitin, cellulose-based compounds, starch, derivatized starch, and the like. These generally will have repeating glucose units as a major portion of the polysaccharide backbone.

Polymerization of a hydrogel can be initiated by a persulfate. The persulfate can be any water-soluble persulfate. Non-limiting examples of water soluble persulfates are ammonium persulfate and alkali metal persulfates. Alkali metals include lithium, sodium and potassium. In some preferred embodiments, the persulfate is ammonium persulfate or potassium persulfate, more preferably, it is ammonium persulfate.

Polymerization of a hydrogel can be accelerated by an accelerant. The accelerant can be a tertiary amine. The tertiary amine can be any water-soluble tertiary amine. Preferably, the tertiary amine is N,N,N′,N′tetramethylethylenediamine or 3-dimethylamino)propionitrile, more preferably it is N,N,N′,N′tetramethylethylenediamine (TEMED).

5.4. Hydrogel Particles

In one aspect, a hydrogel particle of the disclosure comprises a hydrogel and is produced by polymerizing a droplet (see FIG. 2). Microfluidic methods of producing a plurality of droplets, including fluidic and rigidified droplets, are known, and described in US Patent Publication No. 2011/0218123 and U.S. Pat. No. 7,294,503, incorporated herein by reference in their entireties. Such methods provide for a plurality of droplets containing a first fluid and being substantially surrounded by a second fluid, where the first fluid and the second fluid are substantially immiscible (e.g., droplets containing an aqueous-based liquid being substantially surrounded by an oil based liquid).

A plurality of fluidic droplets (e.g., prepared using a microfluidic device) may be polydisperse (e.g., having a range of different sizes), or in some cases, the fluidic droplets may be monodisperse or substantially monodisperse, e.g., having a homogenous distribution of diameters, for instance, such that no more than about 10%, about 5%, about 3%, about 1%, about 0.03%, or about 0.01% of the droplets have an average diameter greater than about 10%, about 5%, about 3%, about 1%, about 0.03%, or about 0.01% of the average diameter. The average diameter of a population of droplets, as used herein, refers to the arithmetic average of the diameters of the droplets.

Accordingly, the disclosure provides population of hydrogel particles comprising a plurality of hydrogel particles, wherein the population of hydrogel particles is substantially monodisperse.

The term microfluidic refers to a device, apparatus or system including at least one fluid channel having a cross-sectional dimension of less than 1 mm, and a ratio of length to largest cross-sectional dimension perpendicular to the channel of at least about 3:1. A microfluidic device comprising a microfluidic channel is especially well suited to preparing a plurality of monodisperse droplets.

Non-limiting examples of microfluidic systems that may be used with the present invention are disclosed in U.S. patent application Ser. No. 11/246,911, filed Oct. 7, 2005, entitled “Forming and Control of Fluidic Species,” published as U.S. Patent Application Publication No. 2006/0163385 on Jul. 27, 2006; U.S. patent application Ser. No. 11/024,228, filed Dec. 28, 2004, entitled “Method and Apparatus for Fluid Dispersion,” published as U.S. Patent Application Publication No. 2005/0172476 on Aug. 11, 2005; U.S. patent application Ser. No. 11/360,845, filed Feb. 23, 2006, entitled “Electronic Control of Fluidic Species,” published as U.S. Patent Application Publication No. 2007/000342 on Jan. 4, 2007; International Patent Application No. PCT/US2006/007772, filed Mar. 3, 2006, entitled “Method and Apparatus for Forming Multiple Emulsions,” published as WO 2006/096571 on Sep. 14, 2006; U.S. patent application Ser. No. 11/368,263, filed Mar. 3, 2006, entitled “Systems and Methods of Forming Particles,” published as U.S. Patent Application Publication No. 2007/0054119 on Mar. 8, 2007; U.S. Provisional Patent Application Ser. No. 60/920,574, filed Mar. 28, 2007, entitled “Multiple Emulsions and Techniques for Forming”; and International Patent Application No. PCT/US2006/001938, filed Jan. 20, 2006, entitled “Systems and Methods for Forming Fluidic Droplets Encapsulated in Particles Such as Colloidal Particles,” published as WO 2006/078841 on Jul. 27, 2006, each incorporated herein by reference.

Droplet size is related to microfluidic channel size. The microfluidic channel may be of any size, for example, having a largest dimension perpendicular to fluid flow of less than about 5 mm or 2 mm, or less than about 1 mm, or less than about 500 μm, less than about 200 μm, less than about 100 μm, less than about 60 μm, less than about 50 μm, less than about 40 μm, less than about 30 μm, less than about 25 μm, less than about 10 μm, less than about 3 μm, less than about 1 μm, less than about 300 nm, less than about 100 nm, less than about 30 nm, or less than about 10 nm.

Droplet size can be tuned by adjusting the relative flow rates. In some embodiments, drop diameters are equivalent to the width of the channel, or within about 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% the width of the channel.

The dimensions of a hydrogel particle of the disclosure are substantially similar to the droplet from which it was formed. Therefore, in some embodiments, a hydrogel particle has a diameter of less than about 1 μm, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 600, 800, or less than 1000 μm in diameter. In some embodiments, a hydrogel particle has a diameter of more than about 1 μm, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 600, 800, or greater than 1000 μm in diameter. In typical embodiments, a hydrogel particle has a diameter in the range of 5 μm to 100 μm.

In some embodiments, a hydrogel particle of the disclosure is spherical in shape.

In some embodiments, a hydrogel particle of the disclosure has material modulus properties (e.g., elasticity) more closely resembling that of a target cell as compared to a polystyrene bead of the same diameter.

In some embodiments, a hydrogel particle of the disclosure does not comprise agarose.

5.5. Optical Properties

5.5.1 Passive Optical Properties

The three primary modes of deconvolution for flow cytometry are the two passive optical properties of a particle (forward scattering, FSC, corresponding to the refractive index, or RI; and side scattering, SSC) and biomarkers present on the surface of a given cell type. Therefore, compositions that allow hydrogel particles of the disclosure to mimic specific cell types with respect to these three modes are useful for providing synthetic, robust calibrants for flow cytometry.

In some embodiments, the refractive index (RI) of a disclosed hydrogel particle is greater than about 1.10, greater than about 1.15, greater than about 1.20, greater than about 1.25, greater than about 1.30, greater than about 1.35, greater than about 1.40, greater than about 1.45, greater than about 1.50, greater than about 1.55, greater than about 1.60, greater than about 1.65, greater than about 1.70, greater than about 1.75, greater than about 1.80, greater than about 1.85, greater than about 1.90, greater than about 1.95, greater than about 2.00, greater than about 2.10, greater than about 2.20, greater than about 2.30, greater than about 2.40, greater than about 2.50, greater than about 2.60, greater than about 2.70, greater than about 2.80, or greater than about 2.90.

In some embodiments, the refractive index (RI) of a disclosed hydrogel particle is less than about 1.10, less than about 1.15, less than about 1.20, less than about 1.25, less than about 1.30, less than about 1.35, less than about 1.40, less than about 1.45, less than about 1.50, less than about 1.55, less than about 1.60, less than about 1.65, less than about 1.70, less than about 1.75, less than about 1.80, less than about 1.85, less than about 1.90, less than about 1.95, less than about 2.00, less than about 2.10, less than about 2.20, less than about 2.30, less than about 2.40, less than about 2.50, less than about 2.60, less than about 2.70, less than about 2.80, or less than about 2.90.

The SSC of a disclosed hydrogel particle is most meaningfully measured in comparison to that of target cell. In some embodiments, a disclosed hydrogel particle has an SSC within 30%, within 25%, within 20%, within 15%, within 10%, within 5%, or within 1% that of a target cell, as measured by a cytometric device.

The FSC of a disclosed hydrogel particle is most meaningfully measured in comparison to that of target cell. In some embodiments, a disclosed hydrogel particle has an FSC within 30%, within 25%, within 20%, within 15%, within 10%, within 5%, or within 1% that of a target cell, as measured by a cytometric device.

SSC can be tuned for a hydrogel by incorporating a high-refractive index molecule in the hydrogel. Preferred high-refractive index molecules include colloidal silica, alkyl acrylate and alkyl methacrylate. Thus in some embodiments, a hydrogel particle of the disclosure comprises alkyl acrylate and/or alkyl methacrylate.

Alkyl acrylates or Alkyl methacrylates can contain 1 to 18, 1 to 8, or 2 to 8, carbon atoms in the alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, 2-ethylhexyl, heptyl or octyl groups. The alkyl group may be branched or linear.

High-refractive index molecules can also include vinylarenes such as styrene and methylstyrene, optionally substituted on the aromatic ring with an alkyl group, such as methyl, ethyl or tert-butyl, or with a halogen, such as chlorostyrene.

In some embodiments, FSC is modulated by adjusting the percentage of monomer present in the composition thereby altering the water content present during hydrogel formation.

FSC is related to particle volume, and thus can be modulated by altering particle diameter, as described herein.

SSC can be engineered by encapsulating nanoparticles within hydrogels to mimic organelles in a target cell. In some embodiments, a hydrogel particle of the disclosure comprises one or more types of nanoparticles selected from the group consisting of: polymethyl methacrylate (PMMA) nanoparticles, polystyrene (PS) nanoparticles, and silica nanoparticles.

5.5.2 Functionalization of Hydrogel Particles

Hydrogel particles can be functionalized, allowing them to mimic optical properties of labeled cells. In some embodiments, a hydrogel particle comprises a bifunctional monomer, and functionalization of the hydrogel particle occurs via the bifunctional monomer. In typical embodiments, a functionalized hydrogel particle comprises a free amine group.

A hydrogel particle can be functionalized with any fluorescent dye known in the art, including fluorescent dyes listed in The MolecularProbes® Handbook—A Guide to Fluorescent Probes and LabelingTechnologies, incorporated herein by reference in its entirety. Functionalization can be mediated by a compound comprising a free amine group, e.g. allylamine, which can be incorporated into a hydrogel particle during the formation process.

Non-limiting examples of known fluorescent dyes include: 6-carboxy-4′,5′-dichloro-2′,7′-dimethoxyfluorescein succinimidylester; 5-(and-6)-carboxyeosin; 5-carboxyfluorescein; 6-carboxyfluorescein; 5-(and-6)-carboxyfluorescein; 5-carboxyfluorescein-bis-(5-carboxymethoxy-2-nitrobenzyl)ether, -alanine-carboxamide, or succinimidyl ester; 5-carboxyfluoresceinsuccinimidyl ester; 6-carboxyfluorescein succinimidyl ester; 5-(and-6)-carboxyfluorescein succinimidyl ester; 5-(4,6-dichlorotriazinyl) amino fluorescein; 2′,7′-difluorofluorescein; eosin-5-isothiocyanate; erythrosin5-isothiocyanate; 6-(fluorescein-5-carboxamido)hexanoic acid or succinimidyl ester; 6-(fluorescein-5-(and-6)-carboxamido)hexanoic acid or succinimidylester; fluorescein-5-EX succinimidyl ester; fluorescein-5-isothiocyanate; fluorescein-6-isothiocyanate; OregonGreen® 488 carboxylic acid, or succinimidyl ester; Oregon Green® 488isothiocyanate; Oregon Green® 488-X succinimidyl ester; Oregon Green®500 carboxylic acid; Oregon Green® 500 carboxylic acid, succinimidylester or triethylammonium salt; Oregon Green® 514 carboxylic acid; Oregon Green® 514 carboxylic acid or succinimidyl ester; RhodamineGreen™ carboxylic acid, succinimidyl ester or hydrochloride; Rhodamine Green™ carboxylic acid, trifluoroacetamide or succinimidylester; Rhodamine Green™-X succinimidyl ester or hydrochloride; RhodolGreen™ carboxylic acid, N,O-bis-(trifluoroacetyl) or succinimidylester; bis-(4-carboxypiperidinyl)sulfonerhodamine or di(succinimidylester); 5-(and-6)carboxynaphthofluorescein, 5-(and-6)carboxynaphthofluorescein succinimidyl ester; 5-carboxyrhodamine 6G hydrochloride; 6-carboxyrhodamine6Ghydrochloride, 5-carboxyrhodamine 6G succinimidyl ester; 6-carboxyrhodamine 6G succinimidyl ester; 5-(and-6)-carboxyrhodamine6G succinimidyl ester; 5-carboxy-2′,4′,5′,7′-tetrabromosulfonefluorescein succinimidyl ester or bis-(diisopropylethylammonium) salt; 5-carboxytetramethylrhodamine; 6-carboxytetramethylrhodamine; 5-(and-6)-carboxytetramethylrhodamine; 5-carboxytetramethylrhodamine succinimidyl ester; 6-carboxytetramethylrhodamine succinimidyl ester; 5-(and-6)-carboxytetramethylrhodamine succinimidyl ester; 6-carboxy-X-rhodamine; 5-carboxy-X-rhodamine succinimidyl ester; 6-carboxy-Xrhodamine succinimidyl ester; 5-(and-6)-carboxy-Xrhodaminesuccinimidyl ester; 5-carboxy-X-rhodamine triethylammonium salt; Lissamine™ rhodamine B sulfonyl chloride; malachite green; isothiocyanate; NANOGOLD® mono(sulfosuccinimidyl ester); QSY® 21carboxylic acid or succinimidyl ester; QSY® 7 carboxylic acid or succinimidyl ester; Rhodamine Red™-X succinimidyl ester; 6-(tetramethylrhodamine-5-(and-6)-carboxamido)hexanoic acid; succinimidyl ester; tetramethylrhodamine-5-isothiocyanate; tetramethylrhodamine-6-isothiocyanate; tetramethylrhodamine-5-(and-6)-isothiocyanate; Texas Red® sulfonyl; Texas Red® sulfonyl chloride; Texas Red®-X STP ester or sodium salt; Texas Red®-X succinimidyl ester; Texas Red®-X succinimidyl ester; and X-rhodamine-5-(and-6)-isothiocyanate.

Other examples of fluorescent dyes include BODIPY® dyes commercially available from Invitrogen, including, but not limited to BODIPY® FL; BODIPY® TMR STP ester; BODIPY® TR-X STP ester; BODIPY® 630/650-X STPester; BODIPY® 650/665-X STP ester; 6-dibromo-4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid succinimidyl ester; 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-3,5-dipropionic acid; 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoicacid; 4,4-difluoro-5,7-dimethyl-4-bora3a,4a-diaza-s-indacene-3-pentanoicacid succinimidyl ester; 4,4-difluoro-5,7-dimefhyl-4-bora-3a,4a-diaza-s-indacene-3propionicacid; 4,4-difluoro-5,7-dimethyl-4-bora-3a,4adiaza-s-indacene-3-propionicacid succinimidyl ester; 4,4difluoro-5,7-dimefhyl-4-bora-3a,4a-diaza-s-indacene-3propionic acid; sulfosuccinimidyl ester or sodium salt; 64(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3propionyl)amino)hexanoicacid; 6-((4,4-difluoro-5,7dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl)amino)hexanoic acid or succinimidyl ester; N-(4,4-difluoro5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-propionyl)cysteic acid, succinimidyl ester or triethylammonium salt; 6-4,4-difluoro-1,3-dimethyl-5-(4-methoxyphenyl)-4-bora3a,4a4,4-difluoro-5,7-diphenyl-4-bora-3a,4a-diaza-s-indacene-3-propionicacid; 4,4-difluoro-5,7-diphenyl-4-bora3a,4a-diaza-s-indacene-3-propionicacid succinimidyl ester; 4,4-difluoro-5-phenyl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid; succinimidyl ester; 6-((4,4-difluoro-5-phenyl-4bora-3a,4a-diaza-s-indacene-3-propionyl)amino)hexanoicacid or succinimidyl ester; 4,4-difluoro-5-(4-phenyl-1,3butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-propionicacid succinimidyl ester; 4,4-difluoro-5-(2-pyrrolyl)-4-bora-3a,4a-diaza-s-indacene-3-propionic acid succinimidyl ester; 6-4(4,4-difluoro-5-(2-pyrrolyl)-4-bora-3a,4a-diaza-s-indacene-3-yl)styryloxy)acetyl)aminohexanoicacid or succinimidyl ester; 4,4-difluoro-5-styryl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid; 4,4-difluoro-5-styryl-4-bora-3a,4a-diaza-s-indacene-3-propionic acid; succinimidyl ester; 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-propionicacid; 4,4-difluoro-1,3,5,7-tetramethyl-4bora-3a,4a-diaza-s-indacene-8-propionicacid succinimidyl ester; 4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3-propionicacid succinimidyl ester; 6-(((4-(4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diazas-indacene-3-yl)phenoxy)acetyl)amino)hexanoic acid or succinimidyl ester; and 6-(((4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza-s-indacene-3-yl)styryloxy)acetyl)aminohexanoicacid or succinimidyl ester.

Fluorescent dyes can also include for example, Alexa fluor dyes commercially available from Invitrogen, including but not limited to Alexa Fluor® 350 carboxylic acid; Alexa Fluor® 430 carboxylic acid; Alexa Fluor® 488 carboxylic acid; Alexa Fluor® 532 carboxylic acid; Alexa Fluor® 546 carboxylic acid; Alexa Fluor® 555 carboxylic acid; Alexa Fluor® 568 carboxylic acid; Alexa Fluor® 594 carboxylic acid; Alexa Fluor® 633 carboxylic acid; Alexa Fluor® 647 carboxylic acid; Alexa Fluor® 660 carboxylic acid; and Alexa Fluor® 680 carboxylic acid. Fluorescent dyes the present invention can also be, for example, cyanine dyes commercially available from Amersham-Pharmacia Biotech, including, but not limited to Cy3 NHS ester; Cy 5 NHS ester; Cy5.5 NHSester; and Cy7 NHS ester.

5.6. Target Cells

Hydrogel particles of the disclosure behave similarly to target cells in procedures such as staining and analysis by flow cytometry or FACS.

In some embodiments, a target cell is an immune cell. Non-limiting examples of immune cells include B lymphocytes, also called B cells, T lymphocytes, also called T cells, natural killer (NK) cells, lymphokine-activated killer (LAK) cells, monocytes, macrophages, neutrophils, granulocytes, mast cells, platelets, Langerhans cells, stem cells, dendritic cells, peripheral blood mononuclear cells, tumor infiltrating (TIL) cells, gene modified immune cells including hybridomas, drug modified immune cells, and derivatives, precursors or progenitors of any of the cell types listed herein.

In some embodiments, a target cell encompasses all cells of a particular class of cell with shared properties. For example, a target cell can be a lymphocyte, including NK cells, T cells, and B cells. A target cell can be an activated lymphocyte.

In some embodiments, a target cell is a primary cell, cultured cell, established cell, normal cell, transformed cell, infected cell, stably transfected cell, transiently transfected cell, proliferating cell, or terminally differentiated cells.

In one embodiment, a target cell is a primary neuronal cell. A variety of neurons can be target cells. As non-limiting examples, a target cell can be a primary neuron; established neuron; transformed neuron; stably transfected neuron; or motor or sensory neuron.

In other embodiments, a target cell is selected from the group consisting of: primary lymphocytes, monocytes, and granulocytes.

A target cell can be virtually any type of cell, including prokaryotic and eukaryotic cells.

Suitable prokaryotic target cells include, but are not limited to, bacteria such as E. coli, various Bacillus species, and the extremophile bacteria such as thermophiles.

Suitable eukaryotic target cells include, but are not limited to, fungi such as yeast and filamentous fungi, including species of Saccharomyces, Aspergillus, Trichoderma, and Neurospora; plant cells including those of corn, sorghum, tobacco, canola, soybean, cotton, tomato, potato, alfalfa, sunflower, etc.; and animal cells, including fish, birds and mammals. Suitable fish cells include, but are not limited to, those from species of salmon, trout, tilapia, tuna, carp, flounder, halibut, swordfish, cod and zebrafish. Suitable bird cells include, but are not limited to, those of chickens, ducks, quail, pheasants and turkeys, and other jungle foul or game birds. Suitable mammalian cells include, but are not limited to, cells from horses, cows, buffalo, deer, sheep, rabbits, rodents such as mice, rats, hamsters and guinea pigs, goats, pigs, primates, marine mammals including dolphins and whales, as well as cell lines, such as human cell lines of any tissue or stem cell type, and stem cells, including pluripotent and non-pluripotent, and non-human zygotes.

Suitable cells also include those cell types implicated in a wide variety of disease conditions, even while in a non-diseased state. Accordingly, suitable eukaryotic cell types include, but are not limited to, tumor cells of all types (e.g., melanoma, myeloid leukemia, carcinomas of the lung, breast, ovaries, colon, kidney, prostate, pancreas and testes), cardiomyocytes, dendritic cells, endothelial cells, epithelial cells, lymphocytes (T-cell and B cell), mast cells, eosinophils, vascular intimal cells, macrophages, natural killer cells, erythrocytes, hepatocytes, leukocytes including mononuclear leukocytes, stem cells such as haemopoetic, neural, skin, lung, kidney, liver and myocyte stem cells (for use in screening for differentiation and de-differentiation factors), osteoclasts, chondrocytes and other connective tissue cells, keratinocytes, melanocytes, liver cells, kidney cells, and adipocytes. In certain embodiments, the cells are primary disease state cells, such as primary tumor cells. Suitable cells also include known research cells, including, but not limited to, Jurkat T cells, NIH3T3 cells, CHO, COS, etc. See the ATCC cell line catalog, hereby expressly incorporated by reference.

In some embodiments, a target cell is a tumor microvesicle or tumor macrovesicle. Tumor microvesicles, also known as tumor-secreted microvesicles or tumor-secreted exosomes, can be found in circulating blood and may have immune-suppressive activities. Tumor microvesicles typically range in size from 30-200 nm in diameter. Larger tumor microvesicles may be referred to as tumor macrovesicles, and can range in size from 3-10 μm in diameter.

6. EXAMPLES Example 1 Generation of Hydrogel Particles

Photomasks for UV lithography were sourced from CADart Services Inc. and were designed using AutoCad (AutoDesk, Inc.). SU-8 photo resist (Microchem, Inc.) was photo crosslinked on 4″ silicon wafers using a collimated UV light source (OAI, Inc.) to create masters for microfluidic device fabrication. PDMS (polydimethylsiloxane, Sigma Aldrich, Inc.) was prepared and formed using standard published methods for soft lithography and microfluidic device fabrication (See, McDonald J C, et al., 2000, Electrophoresis 21:27-40).

Droplets were formed using flow-focusing geometry where two oil channels focus a central stream of aqueous monomer solution to break off droplets in a water-in-oil emulsion. A fluorocarbon-oil (Novec 7500 3M, Inc.) was used as the outer, continuous phase liquid for droplet formation. To stabilize droplets before polymerization, a surfactant was added at 0.5% w/w to the oil phase (ammonium carboxylate salt of Krytox 157 FSH, Dupont). To make the basic polyacrylamide gel particle, a central phase of an aqueous monomer solution containing N-acrylamide (1-20% w/v), a cross-linker (N,N′-bisacrylamide, 0.05-1% w/v), an accelerator, and ammonium persulfate (1% w/v) was used. An accelerator, (N,N,N′,N′-tetramethylethylenediamine 2% vol %) was added to the oil-phase in order to trigger hydrogel particle polymerization after droplet formation.

Several co-monomers were added to the basic gel formulation to add functionality. Allyl-amine provided primary amine groups for secondary labeling after gel formation. We modulated forward scatter by adjusting the refractive index of the gel by adding co-monomers allyl acrylate and allyl methacrylate. Side scattering of the droplets was tuned by adding a colloidal suspension of silica nanoparticles and/or PMMA (poly(methyl methacrylate)) particles (˜100 nm) to the central aqueous phase prior to polymerization.

Stoichiometric multiplexing of the hydrogel particles was achieved by utilizing co-monomers containing chemically orthogonal side groups (amine, carboxyl, maleimide, epoxide, alkyne, etc.) for secondary labeling.

Droplets were formed at an average rate of 5 kHz and were collected in the fluorocarbon oil phase. Polymerization was completed at 50° C. for 30 minutes, and the resulting hydrogel particles were washed from the oil into an aqueous solution.

Example 2 Generation and Visualization of 12 μm Hydrogel Particles

Water containing 5% acrylamide, 0.25% bisacrylamide, 0.05% allyl amine, and 0.1% ammonium persulfate was flowed through a center channel and focused by oil containing 0.1% TEMED through a 10 micron nozzle to produce 10 μm hydrogel particles, shown in FIG. 3A. Following polymerization, the particles were washed in water, shown in FIG. 3B, and conjugated to dyes of interest. The fluorescent hydrogel particles were visualized with fluorescence microscopy, shown in FIG. 3C.

Example 3 Multidimensional Tuning of Hydrogel Particle Optical Properties

As depicted in FIG. 4, hydrogel particles are tuned in multiple dimensions to match specific cell types unlike polystyrene beads. Cells are deconvolved using combinations of optical parameters such as FSC and SSC (FIG. 4A) or secondary markers. Hydrogel particles are tuned to exactly match the SSC and FSC of specific cell types unlike polystyrene beads (brown) which are limited in size (FSC) and side scattering (FIG. 4B). Hydogel particles are further functionalized with stoiochiometrically tuned ratios of specific chemical side-groups and secondary labels allowing any cell type to be precisely matched without suffering from biological noise as fixed cell lines do (FIG. 4C).

Example 4 Flow Cytometer Delay Time as a Function of Hydrogel Particle Diameter

As shown in FIG. 5, the inter-drop delay for a flow cytometer can be precisely correlated to hydrogel particle diameter. Data are shown for hydrogel particles of 3, 6, 10, 32, and 50 μm diameters using flow cytometer nozzle sizes of 70 and 100 μm.

Example 5 Comparison of Hydrogel Particles with Encapsulated DNA to Cells

To form hydrogel particles with encapsulated DNA, 40 μg/mL-1000 μg/mL of reconstituted calf thymus DNA was added to a polymer mix containing 20% 19:1(acrylamide:bis-acrylamide) and 0.1% allyl amine in water. 0.4% ammonium persulfate was added to the mix prior to droplet formation. Hydrogel particles were formed as described in Example 1. Hydrogel particles with 200 μg/mL of encapsulated calf thymus DNA displayed cell-like staining using propidium iodide as visualized using a commercial imaging cytometer and compared to Chinese Hamster Ovary cells stained using the same procedure. Images were obtained using a Nexcelom Cellometer™ (FIG. 6).

Cells obtained from a buccal swab were washed in PBS and stained with propidium iodide. In parallel, populations of hydrogel particles containing a range of DNA concentrations were also stained in the same manner. Both the cell and particle suspensions were analyzed on a flow cytometer (488/590 nm excitation/emission). Flow cytometry analysis of cheek cells and the same range of encapsulated DNA particles showed that the particles display a range of cell-like fluorescent properties (FIG. 7, left panel). The intensity of staining shows a linear correlation with the median intensity as measured by flow cytometry (FIG. 7, right panel).

Example 6 Tuning of Hydrogel Particle Side Scattering

Colloidal silica was added at 12.5%, 6.25%, 3.125% and 0% to the aqueous fraction of the polymer mix and hydrogel particles were formed as described in Example 1. Forward and side scattering data were obtained using a flow cytometer. The results showed that side scatter signal (FIG. 8, left panel) increased with higher percentages of encapsulated nanoparticles while forward scatter (FIG. 8, right panel) remained generally unchanged, demonstrating the independent tuning of side scatter and forward scatter.

Example 7 Tuning of Hydrogel Particle Forward Scattering

In this experiment, the percentage of acrylamide:bis-acrylamide in the hydrogel composition was varied from between 10 and 40% to tune the refractive index of the hydrogel particles as measured by forward scattering in a flow cytometer. As shown in FIG. 9, the forward scattering increased with increasing percentages of acrylamide:bis-acrylamide as a fraction of water.

All publications, patents, patent applications and other documents cited in this application are hereby incorporated by reference in their entireties for all purposes to the same extent as if each individual publication, patent, patent application or other document were individually indicated to be incorporated by reference for all purposes.

While various specific embodiments have been illustrated and described, it will be appreciated that various changes can be made without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A composition comprising a hydrogel particle, wherein the hydrogel particle has at least one optical property substantially similar to that of a target cell, wherein the optical property is measured by a cytometric device.
 2. The composition of claim 1, wherein the hydrogel particle has an SSC within 10% of that of a target cell, as measured by a cytometric device.
 3. The composition of claim 1, wherein the hydrogel particle has an FSC within 10% of that of a target cell, as measured by a cytometric device.
 4. The composition of claim 1, wherein the hydrogel particle has a refractive index of greater than about 1.15.
 5. The composition of claim 1, wherein the hydrogel particle has a refractive index of greater than about 1.3.
 6. The composition of claim 1, wherein the hydrogel particle has a refractive index of greater than about 1.7.
 7. The composition of claim 1, wherein the hydrogel particle has a diameter of less than about 30 μm.
 8. The composition of claim 7, wherein the hydrogel particle has a diameter of less than about 10 μm.
 9. The composition of claim 8, wherein the hydrogel particle has a diameter of less than about 1 μm.
 10. The composition of claim 1, wherein the hydrogel particle comprises colloidal silica.
 11. The composition of claim 1, wherein the hydrogel particle is functionalized.
 12. The composition of claim 11, wherein the hydrogel particle comprises a free amine group.
 13. The composition of claim 12, wherein the hydrogel particle comprises allyl amine.
 14. The composition of claim 1, wherein the target cell is an immune cell, eukaryotic cell, or bacteria.
 15. The composition of claim 1, wherein the hydrogel particle is produced by polymerizing a droplet.
 16. A population of hydrogel particles comprising a plurality of hydrogel particles, wherein each of the hydrogel particles has at least one optical property substantially similar to that of a target cell, wherein the population of hydrogel particles is substantially monodisperse.
 17. The population of hydrogel particles of claim 16, wherein no more than 10% of the hydrogel particles have an average diameter greater than about 10% of the average diameter of the population of hydrogel particles.
 18. The population of hydrogel particles of claim 17, wherein no more than 5% of the hydrogel particles have an average diameter greater than about 5% of the average diameter of the population of hydrogel particles.
 19. A method of calibrating a cytometric device for analysis of a target cell, the method comprising a) inserting into the device a hydrogel particle having optical properties substantially similar to the optical properties of the target cell; b) measuring the optical properties of the hydrogel particle using the cytometric device. 